Multicast routing method and apparatus for routing multicast packet

ABSTRACT

A communications apparatus for converting an IPv4 multicast packet transmit from an IPv4 terminal into an IPv6 multicast packet and transmitting the converted IPv6 multicast packet to one of a plurality of IPv6 networks. The communications apparatus has information indicating to which IPv6 network the IPv4 multicast packet to undergo conversion processing is to be transmitted. The communications apparatus then converts the received IPv4 multicast packet into an IPv6 multicast packet and transmits the converted IPv6 multicast packet to an IPv6 network where it is required to be sent.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application relates to U.S. Pat. application Ser. No.09/257003 filed on Feb. 25, 1999 based on Japanese Patent ApplicationNumber 10-046739 filed on Feb. 27, 1998 and U.S. Pat. application Ser.No. 09/614715 filed on Jul. 6, 2000 based on Japanese Patent ApplicationNumber 8-291480 and 9-212889 and U.S. Pat. application Ser. No.09/421275 filed on Oct. 20, 1999 based on Japanese Patent ApplicationNumber 10-299613, all of which are assigned to the present assignee. Thecontents of those applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a multicast routing method andapparatus for routing a multicast packet and more particularly to amulticast routing method and apparatus for realizing multicastcommunication between an IPv4 terminal using IPv4 (Internet Protocolversion 4) as a communication protocol and an IPv6 terminal using IPv6(Internet Protocol version 6) as a communication protocol.

[0003] In recent years, it has been feared that the 32-bit address spaceon networks provided by the IPv4, if left alone, will soon be used up.To avoid the possible exhaustion of the address space, the IPv6, thenext version of IPv4, has been developed and is drawing attention as ameans for networking new terminals (for example, mobile IP terminals).

[0004] An example method for establishing communication between IPv4terminals based on the IPv4 protocol and IPv6 terminals based on theIPv6 protocol is a technique disclosed in Japanese Patent UnexaminedPublication No. 10-136052. The Japanese Patent Unexamined PublicationNo. 10-136052 describes that a DNS (Domain Name System) protocolextension technology incorporated into a device installed in acommunication path generates an IP address conversion table that managesthe correspondence between IPv4 addresses and IPv6 addresses and, basedon the IP address conversion table, performs conversion between an IPv4header and an IPv6 header. The use of this technology disclosed in theofficial gazette enables communication between IPv4 terminals and IPv6terminals.

SUMMARY OF THE INVENTION

[0005] Although the technology described above can perform IP unicastcommunication between IPv4 terminals and IPv6 terminals, it cannotestablish IP multicast communication between them. Here, it should benoted that the unicast signifies one-to-one communication and themulticast signifies communication from one source node to specifiedmultiple destination nodes (communication within a particular group).

[0006] An object of the present invention is to provide a multicastrouting method and apparatus which enables IPv6 terminals to receive anIPv4 multicast packet transmit from an IPv4 terminal and also enablesIPv4 terminals to receive an IPv6 multicast packet transmit from an IPv6terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is an example configuration diagram of a conversion device1 according to the present invention.

[0008]FIG. 2 is a configuration diagram of an IPv4 unicast address table31.

[0009]FIG. 3 is a configuration diagram of an IPv6 unicast address table32.

[0010]FIG. 4 is a configuration diagram of an IP address conversiontable 41.

[0011]FIG. 5 is a configuration diagram of an IP multicast pathinformation table 51.

[0012]FIG. 6 is a configuration diagram of an IPv4 adjoining routerinformation table 71.

[0013]FIG. 7 is a configuration diagram of an IPv6 adjoining routerinformation table 72.

[0014]FIG. 8 is a configuration diagram of an IPv4 multicast memberinformation table 61.

[0015]FIG. 9 is a configuration diagram of an IPv6 multicast memberinformation table 62.

[0016]FIG. 10 is a configuration diagram showing a communicationsnetwork system 100 using the conversion device 1 according to thepresent invention.

[0017]FIG. 11 is a configuration diagram showing a communicationsnetwork system 200 using the conversion device 1 according to thepresent invention.

[0018]FIG. 12 is a communication sequence diagram for steps 201, 202.

[0019]FIG. 13 is a communication sequence diagram for steps 203, 204.

[0020]FIG. 14 is a communication sequence diagram for steps 205-207.

[0021]FIG. 15 is a communication sequence diagram for steps 208, 209.

[0022]FIG. 16 is a communication sequence diagram for steps 210-214.

[0023]FIG. 17 is a communication sequence diagram for step 215.

[0024]FIG. 18 is a communication sequence diagram for step 217.

[0025]FIG. 19 is a communication sequence diagram for steps 231-233.

[0026]FIG. 20 is a communication sequence diagram for step 234.

[0027]FIG. 21 is a communication sequence diagram for steps 235-237.

[0028]FIG. 22 is a communication sequence diagram for step 238.

[0029]FIG. 23 is an example of hardware configuration diagram for theconversion device 1 according to the invention.

[0030]FIGS. 24A and 24B illustrate formats of an IPv6 header and an IPv4header.

DESCRIPTION OF THE EMBODIMENTS

[0031] Now, embodiments of the present invention will be described indetail by referring to the accompanying drawings.

[0032]FIG. 1 shows one example configuration of the conversion device 1according to the invention. The conversion device 1 is connected, forexample, to IPv4 networks 111, 112 and IPv6 networks 121, 122. Theconversion device 1 establishes the IP multicast communication betweenthe IPv4 terminals and the IPv6 terminals by performing an IP headerconversion on an IPv4 multicast packet and an IPv6 multicast packetdescribed later. The conversion device 1 has an IPtransmission/reception module 2, a conversion IP address holding module3, an IP address conversion information holding module 4, an IP headerconversion module 5, an IP multicast routing control informationmanagement module 6, an IP multicast membership information managementmodule 7, and interfaces 8-11. The interfaces 8-11 refer to pointsthrough which the IP transmission/reception module 2 is connected to theIPv4 networks 111, 112 and the IPv6 networks 121, 122.

[0033] The IP transmission/reception module 2 transmits/receives androutes the IPv4 packet to and from the IPv4,networks 111, 112 and alsothe IPv6 packet to and from the IPv6 networks 121, 122.

[0034] The conversion IP address holding module 3 holds IPv4 unicastaddresses and IPv6 unicast addresses, both used for an IP headerconversion described later. The IPv4 unicast addresses and the IPv6unicast addresses to be used for the IP header conversion are enteredinto the conversion device 1 in advance by an administrator (ormaintenance person) of the conversion device 1. Then, the IPv4 unicastaddresses and the IPv6 unicast addresses are held in an IPv4 unicastaddress table 31 and an IPv6 unicast address table 32, respectively.

[0035]FIG. 2 shows a configuration of the IPv4 unicast address table 31.The IPv4 unicast address table 31 has the IPv4 unicast addresses for IPheader conversion registered in advance according to the input from theadministrator, for example. In FIG. 2, IPv4 addresses 133.144.94.100 to133.144.94.200 are registered as an example.

[0036]FIG. 3 shows a configuration of the IPv6 unicast address table 32.The IPv6 unicast address table 32 has the IPv6 unicast addresses for IPheader conversion registered in advance according to the input from theadministrator, for example. In FIG. 3, IPv6 addresses 4:;100 to 4::200are registered as an example. The IPv4 unicast address table 31 and theIPv6 unicast address table 32 are held in the conversion IP addressholding module 3.

[0037] The IP address conversion information holding module 4 has an IPaddress conversion table 41 which matches the IPv4 addresses and IPv6addresses. The IP address conversion information holding module 4matches IPv4 destination addresses of IPv4 multicast packets transmit bythe IPv4 terminals to IPv6 multicast addresses that allow fixed data(IPv6 multicast prefix) to be added to the IPv4 destination addresses.The IP address conversion information holding module 4 also matches IPv4source addresses of IPv4 multicast packets to IPv6 unicast addressesretrieved from the conversion IP address holding module 3 (if notretrieved yet, the IPv6 unicast addresses are retrieved). Further, theIP address conversion information holding module 4 matches IPv6destination addresses of the IPv6 multicast packets transmit by the IPv6terminals to IPv4 multicast addresses that allow the fixed data (IPv6multicast prefix) to be removed from the IPv6 destination addresses.Further, IP address conversion information holding module 4 matches IPv6source addresses of the IPv6 multicast packets to IPv4 unicast addressesretrieved from the conversion IP address holding module 3 (if notretrieved yet, the IPv4 unicast addresses are retrieved).

[0038]FIG. 4 shows a configuration of the IP address conversion table41. The IP address conversion table 41 matches the IPv4 destinationaddresses of the received IPv4 multicast packets to the associated IPv6multicast addresses (item No. 1 in FIG. 4, for example). The IP addressconversion table 41 matches the IPv4 source addresses of the receivedIPv4 multicast packets to the associated IPv6 unicast addresses (itemNo. 2 in FIG. 4). The IP address conversion table 41 also matches theIPv6 destination addresses of the received IPv6 multicast packets to thecorresponding IPv4 multicast addresses (item No. 3 in FIG. 4). Further,the IP address conversion table 41 matches the IPv6 source addresses ofthe received IPv6 multicast packets to the corresponding IPv4 unicastaddresses (item No. 4 in FIG. 4).

[0039] The IP header conversion module 5 receives through the IPtransmission/reception module 2 an IPv4 multicast packet sent to theconversion device 1 and performs the IP header conversion on the IPv4multicast packet to generate an IPv6 multicast packet. Then, the IPheader conversion module 5 sends the generated IPv6 multicast packet tothe IP transmission/reception module 2. In the IP header conversionprocessing, the IP header conversion module 5 references the IP addressconversion information holding module 4 to retrieve an IPv6 multicastaddress which is related with the IPv4 destination address of the IPv4multicast packet. Then, the IP header conversion module 5 converts theIPv4 destination address of the IPv4 multicast packet into the retrievedIPv6 multicast address. Similarly, the IP header conversion module 5converts an IPv4 source address of the IPv4 multicast packet into anIPv6 source address by referencing the IP address conversion informationholding module 4 to retrieve an IPv6 address corresponding to the IPv4source address and by using the retrieved IPv6 address.

[0040] Further, the IP header conversion module 5 receives through theIP transmission/reception module 2 an IPv6 multicast packet sent to theconversion device 1 and performs the IP header conversion on the IPv6multicast packet to generate an IPv4 multicast packet. Then, the IPheader conversion module 5 refers to the IP address conversioninformation holding module 4 to retrieve IPv4 addresses corresponding tothe destination address and source address of the received IPv6 packetand then completes the conversion from the IPv6 addresses into the IPv4addresses.

[0041]FIG. 24A shows an IPv6 header format. The IPv6 header format hasthe following fields. A “version” field stores “6” which represents theversion number of IPv6. A “priority” field contains a priority level forthe processing performed by routers to forward the packet in thenetwork. A “flow label” field stores an identifier to be used, forexample, in a priority control. A “payload length” field stores a lengthof data part in the packet from which IPv6 header part is removed. A“next header identifier” field stores an identifier indicating, forexample, which upper layer protocol header follows the IPv6 header. A“hop limit” field stores the maximum number of times the packet can betransferred. A “source IP address” field stores source IP addresses anda “destination IP address” field stores destination IP addresses.

[0042]FIG. 24B shows an IPv4 header format. The IPv4 header format hasthe following fields. A “version” field stores “4” which represents theversion number of IPv4. A “header length” field stores a length of theIPv4 header itself. A “service type” field stores informationrepresenting a quality of service provided in the communicationprocessing. A “packet length” field stores an overall size of the packetcomprised of the data block handled by the IP plus the IPv4 header. An“identifier” field stores an identifier used as reference informationwhen transferring data to an upper layer. A “fragment offset” fieldstores control information on packet division. A “flag” field storesinformation indicating where in the original data the divided data(fragment) is located. A “lifetime” field stores the time in which thepacket in question is allowed to exist in the network. A “protocolfield” stores information indicating what the upper layer protocol is. A“header checksum” field stores a checksum of the IP header. Finally, a“source IP address” field contains source IP addresses and a“destination IP address” field contains destination IP addresses.

[0043] The IP header conversion module 5 performs conversion from IPv4header into IPv6 header, shown in FIGS. 24A, 24B, or from IPv6 headerinto IPv4 header, and sets values in the fields in the converted IPv4 orIPv6 header format. In this embodiment, the following descriptionconcerning the IP header conversion processing in particular centers onthe address conversion of the source IP address and the destination IPaddress, i.e., the conversion processing for the “IP source address”field and the “IP destination address” field.

[0044] Based on the IPv4 multicast routing control information and theIPv6 multicast routing control information described later, the IPmulticast routing control information management module 6 determinesrouting destinations of the IPv4 multicast packet and the IPv6 multicastpacket that the conversion device 1 received. The IPv4 multicast routingcontrol information is exchanged with or collected from an IPv4multicast router adjoining the conversion device 1 according to, forexample, the IP multicast routing control protocol and is then held inthe IP multicast routing control information management module 6. As theIP multicast routing control protocol, the PIM-DM (Protocol IndependentMulticast, Dense Mode) protocol described in, for example, the RFC2362and draft-ietfpim-v2-dm-03.txt etc. may be used. Any other appropriateprotocol may also be used.

[0045] The IPv4 multicast routing control information is updated by IPv4multicast group member information notified to the IP multicast routingcontrol information management module 6 from an IP multicast membershipinformation management module 7 described later. Similarly, the IPv6multicast routing control information is also exchanged with orcollected from an IPv6 multicast router adjoining the conversion device1. Then, the IPv6 multicast routing control information is updated byIPv6 multicast group member information notified to the IP multicastrouting control information management module 6 from the IP multicastmembership information management module 7. The IPv4 multicast routingcontrol information and the IPv6 multicast routing control informationare stored in the IP multicast path information table 51. The IPmulticast path information table 51 is stored in the IP multicastrouting control information management module 6 or any other appropriatememory.

[0046]FIG. 5 shows a configuration of the IP multicast path informationtable 51. The IP multicast path information table 51 holds informationon the IP networks that are required to route the IP multicast packettransmit by the IP multicast server, in the form of whether the packetshould be output or not for each of the interfaces 8-11. The IPv4multicast routing control information refers to those of the informationheld in the IP multicast path information table 51 which have their IPv4multicast addresses stored in the “IP multicast address” item. The IPv6multicast routing control information refers to those of the informationheld in the IP multicast path information table 51 which have their IPv6multicast addresses stored in the “IP multicast address” item.

[0047]FIG. 6 shows a configuration of the IPv4 adjoining routerinformation table 71. The IPv4 adjoining router information table 71holds information on IPv4 multicast routers adjoining the conversiondevice 1. In the example shown in FIG. 6, the information on theadjoining router is entered for each interface. For item number “1”, theinformation on the adjoining router corresponding to the interface 8 is“OFF”; for item number “2”, the information on the adjoining routercorresponding to the interface 9 is “OFF”; for item number “3”, theinformation on the adjoining router corresponding to the interface 10 is“OFF”; and for item number “4”, the information on the adjoining routercorresponding to the interface 11 is “OFF”.

[0048]FIG. 7 shows a configuration of the IPv6 adjoining routerinformation table 72. The IPv6 adjoining router information table 72holds information on IPv6 multicast routers adjoining the conversiondevice 1. In the example shown in FIG. 7, the information on theadjoining router is entered for each interface. For item number “1”, theinformation on the adjoining router corresponding to the interface 8 is“OFF”; for item number “2”, the information on the adjoining routercorresponding to the interface 9 is “OFF”; for item number “3”, theinformation on the adjoining router corresponding to the interface 10 is“OFF”; and for item number “4”, the information on the adjoining routercorresponding to the interface 11 is “OFF”.

[0049] In FIG. 6 and FIG. 7, the information on the adjoining routerbeing “ON” means that an operational IPv4 or IPv6 multicast routerexists on the network connected to the interface under consideration.The information on the adjoining router being “OFF” means that anoperational IPv4 or IPv6 multicast router does not exist on the networkconnected to that interface.

[0050] According to an IPv4 multicast group membership protocol, such asthe IGMP (Internet Group Management Protocol) protocol described in RFC(Request For Comments) 2236 of IETF (Internet Engineering Task Force),the IP multicast membership information management module 7 receives arequest to participate in or leave the IPv4 multicast group, which wastransmitted from an IPv4 terminal on the IPv4 network connected with theconversion device 1. Then, the IP multicast membership informationmanagement module 7 collects and manages the IPv4 multicast group memberinformation within the IPv4 network directly connected to the conversiondevice 1 according to the request received and at the same time notifiesthe IPv4 multicast group member information to the IP multicast routingcontrol information management module 6.

[0051] Further, according to an IPv6 multicast group membershipprotocol, such as the MLD (Multicast Listener Discovery) protocoldescribed in the RFC 2710, the IP multicast membership informationmanagement module 7 receives a request to participate in or leave anIPv6 multicast group, which was transmitted from an IPv6 terminal on theIPv6 network connected to the conversion device 1. Then, the IPmulticast membership information management module 7 collects andmanages the IPv6 multicast group member information within the IPv6network directly connected to the conversion device 1 according to therequest received and at the same time notifies the IPv6 multicast groupmember information to the IP multicast routing control informationmanagement module 6.

[0052]FIG. 8 shows a configuration of the IPv4 multicast memberinformation table 61 holding the IPv4 multicast group memberinformation. The IPv4 multicast member information table 61 holdsinformation on the IPv4 network to which an IPv4 terminal participatingin the IPv4 multicast address to be header-converted by the conversiondevice 1 belongs. In the example shown in FIG. 8, the information onregistered members is entered for each interface with an IPv4 multicastaddress (238.0.0.2). In item number “1”, the registered memberinformation for the interface 8 is “OFF”; in item number “2”, theregistered member information for the interface 9 is “ON”; in itemnumber “3”, the registered member information for the interface 10 is“OFF”; and in item number “4”, the registered member information for theinterface 11 is “OFF”. The registered member information being “ON”means that an IPv4 terminal participating in the IPv4 multicast addressexists on the network connected to that interface. The registered memberinformation being “OFF” means that there are no such IPv4 terminals.Hence, in FIG. 8, the IPv4 multicast packet with the destination address(238.0.0.2) is received by the IPv4 terminal on the network 112connected to the interface 9.

[0053]FIG. 9 shows a configuration of the IPv6 multicast memberinformation table 62 holding the IPv6 multicast group memberinformation. The IPv6 multicast member information table 62 holdsinformation on the IPv6 network to which an IPv6 terminal participatingin the IPv6 multicast address to be header-converted by the conversiondevice 1 belongs. In the example shown in FIG. 9, the information onregistered members is entered for each interface with an IPv6 multicastaddress (ffle::238.0.0.1). In item number “1”, the registered memberinformation for the interface 8 is “OFF”; in item number “2”, theregistered member information for the interface 9 is “OFF”; in itemnumber “3”, the registered member information for the interface 10 is“OFF”; and in item number “4”, the registered member information for theinterface 11 is “ON”. The registered member information being “ON” meansthat an IPv6 terminal participating in the IPv6 multicast address existson the network connected to that interface. The registered memberinformation being “OFF” means that there are no such IPv6 terminals.Hence, in FIG. 9, the IPv6 multicast packet with the destination address(ffle::238.0.0.1) is received by the IPv6 terminal on the network 122connected to the interface 11, for example, an IPv6 multicast client104.

[0054]FIG. 23 shows an example hardware configuration of the conversiondevice of FIG. 1. In FIG. 23, the conversion device 1 has a networkinterface 133 for establishing connection with the IPv4 networks 111,112 and IPv6 networks 121, 122, a memory unit 135 including, forexample, RAM131 and ROM132, and a processor 130 for executing a programstored in the memory unit 135 and processing various data stored in thememory unit 135. The network interface 133, the memory unit 135 and theprocessor 130 are interconnected via a bus 134. The conversion device 1may also have other storage devices such as a hard disk drive as thememory unit in addition to RAM 131 and ROM 132. In that case, the harddisk drive is not necessarily connected to the bus 134.

[0055] The IP transmission/reception module 2 shown in FIG. 1 comprisesthe network interface 133 for sending and receiving IP (InternetProtocol) packets, a program stored in the memory unit 135 to operatethe IP transmission/reception module 2, and the processor 130 forexecuting the program, all shown in FIG. 23. Rather than beingcontrolled by the processor 130, the network interface 133 may have aseparate processor and a separate memory unit therein to send or receivepackets to and from the IPv4 network 101 and IPv6 network 102. Thenetwork interface 133 in FIG. 23 establishes connection with individualnetworks through the interfaces 8-11. These interfaces 8-11 are physicalconnections or logical network identification information used by theconversion device 1. The IP transmission/reception module 2 uses theseinterfaces 8-11 to identify the individual networks connected to theinterfaces 8-11.

[0056] The conversion IP address holding module 3, the IP addressconversion information holding module 4, the IP header conversion module5, the IP multicast routing control information management module 6 andthe IP multicast membership information management module 7 shown inFIG. 1 each have their own program for their operation and their ownprocessor 130 for executing the program.

[0057]FIG. 10 shows a configuration of a communications network system100 using the conversion device 1 according to this invention. Thecommunications network system 100 is connected to the IPv4 networks 111,112 and the IPv6 networks 121, 122 through the conversion device 1 (IPv4addresses: 133.144.93.1 and 133.144.95.1 and IPv6 addresses: 1::1 and2::1 are allocated, for example). In the IPv4 network 111 there is anIPv4 multicast server 101 (IPv4 address: 133.144.93.2) for transmittingIPv4-compatible multicast packets. In the IPv4 network 112 there is anIPv4 multicast client 102 (IPv4 address: 133.144.95.2) for receivingIPv4-compatible multicast packets. In the IPv6 network 121 there is anIPv6 multicast server 103 (IPv6 address: 1::2) for transmittingIPv6-compatible multicast packets. In the IPv6 network 122 there is anIPv6 multicast client 104 (IPv6 address: 2::2) for receivingIPv6-compatible multicast packets.

[0058] It is assumed that the IPv4 multicast server 101 is transmittingan IPv4 multicast packet (IPv4 address: 238.0.0.1) to the IPv4 network111 and that the IPv6 multicast server 103 is transmitting an IPv6multicast packet (IPv6 address: ffle::238.0.0.2) to the IPv6 network121. Although in FIG. 10 the IPv4 networks 111, 112 and the IPv6networks 121, 122 are shown to be completely physically separate fromeach other, they may be physically mixed in the same network.

[0059] Next, in this communications network system 100, we will explainabout a case where the IPv4 multicast server 101 transmits the IPv4multicast packet (IPv4 address: 238.0.0.1) to the IPv4 network 111 andthe IPv6 multicast client 104 receives the IPv4 multicast packet.

[0060] First, let us explain about the processing (steps 201-204)periodically performed by the conversion device 1 according to the IGMP(Internet Group Management Protocol) protocol, the MLD (MulticastListener Discovery) protocol and the PIM-DM protocol.

[0061]FIG. 12 is a communication sequence diagram for steps 201, 202.First, step 201 will be described. The IP multicast membershipinformation management module 7 generates an IGMP Query messageaccording to the IGMP protocol and at the same time instructs the IPtransmission/reception module 2 to send the IGMP Query message to theIPv4 networks 111, 112. Then, the IP transmission/reception module 2puts the IGMP Query message out on the IPv4 networks 111, 112. The IGMPQuery message is a message which has one of the IPv4 multicast addressesused by an arbitrary IPv4 multicast group specified before being sentout. The terminals participating in the IPv4 multicast group receive theIGMP Query message and return an IGMP Report message thus reporting thatthere are members of the IPv4 multicast group using the IPv4 multicastaddress.

[0062] Conversely, when the IP transmission/reception module 2 receivesan IGMP Report message dispatched by an IPv4 multicast client throughthe IPv4 network 111 or 112, it transfers the IGMP Report message to theIP multicast membership information management module 7. The IPmulticast membership information management module 7 analyzes the IGMPReport message according to the IGMP protocol and generates an IPv4multicast member information table 61. That is, in the IPv4 multicastmember information table 61, for the entries whose “IPv4 addresses” arethe IPv4 multicast group address requested by the IGMP Report message toparticipate, an interface listed in the registered member informationwhich is connected to the network where the IPv4 multicast client thathas returned the IGM Report message exists is set to “ON”. In this stageof explanation, however, it is assumed that on the IPv4 networks 111,112 there are no members in the IPv4 multicast group using the IPv4multicast address specified by the IGMP Query message. Hence, the IPtransmission/reception module 2 does not receive this IGMP Reportmessage.

[0063] Next, step 202 is explained. IP multicast membership informationmanagement module 7 generates an MLD Query message according to the MLDprotocol and instructs the IP transmission/reception module 2 to sendthe generated MLD Query message out to the IPv6 networks 121, 122. Then,the IP transmission/reception module 2 puts the MLD Query message out onthe IPv6 networks 121, 122. The MLD Query message is a message which hasone of the IPv6 multicast addresses used by an arbitrary IPv6 multicastgroup specified before being sent out. The terminals participating inthe IPv6 multicast group receive the MLD Query message and return an MLDReport message thus reporting that there are members of the IPv6multicast group using the IPv6 multicast address.

[0064] Conversely, when the IP transmission/reception module 2 receivesan MLD Report message dispatched by an IPv6 multicast client through theIPv6 network 121 or 122, it transfers the MLD Report message to the IPmulticast membership information management module 7. The IP multicastmembership information management module 7 analyzes the IGMP Reportmessage according to the MLD protocol and generates an IPv6 multicastmember information table 62. That is, in the IPv6 multicast memberinformation table 62, for the entries whose “IPv6 addresses” are theIPv6 multicast group address requested by the MLD Report message toparticipate, an interface listed in the registered member informationwhich is connected to the network where the IPv6 multicast client thathas returned the MLD Report message exists is set to “ON”. In this stageof explanation, however, it is assumed that on the IPv6 networks 121,122 there are no members in the IPv6 multicast group using the IPv6multicast address specified by the MLD Query message. Hence, the IPtransmission/reception module 2 does not receive this MLD Reportmessage.

[0065]FIG. 13 is a communication sequence diagram for steps 203, 204.First, step 203 will be described. The IP multicast routing controlinformation management module 6 generates a Hello message according tothe PIM-DM protocol and instructs the IP transmission/reception module 2to send the Hello message out to the IPv4 networks 111, 112. Then, theIP transmission/reception module 2 puts the Hello message out on theIPv4 networks 111, 112.

[0066] Conversely, when the IP transmission/reception module 2 receivesa Hello message dispatched by an IPv4 multicast router through the IPv4network 111 or 112, it transfers the Hello message to the IP multicastrouting control information management module 6. The IP multicastrouting control information management module 6 analyzes the Hellomessage according to the PIM-DM protocol and generates an IPv4 adjoiningrouter information table 71. That is, the adjoining router informationfor the interface that has received the Hello message is set to “ON”. Inthis stage of explanation, however, it is assumed that on the IPv4network 111 or 112 there are no IPv4 multicast routers. Hence, the IPtransmission/reception module 2 does not receive this Hello message.

[0067] Next, step 204 will be described. The IP multicast routingcontrol information management module 6 generates a Hello messageaccording to the PIM-DM protocol and instructs the IPtransmission/reception module 2 to send the generated Hello message outto the IPv6 networks 121, 122. Then, the IP transmission/receptionmodule 2 sends the Hello message out to the IPv6 networks 121, 122.

[0068] Conversely, when the IP transmission/reception module 2 receivesa Hello message dispatched by an IPv6 multicast router through the IPv6network 121 or 122, it transfers the Hello message to the IP multicastrouting control information management module 6. The IP multicastrouting control information management module 6 analyzes the Hellomessage according to the PIM-DM protocol and generates an IPv6 adjoiningrouter information table 72. That is, the adjoining router informationfor the interface that has received the Hello message is set to “ON”. Inthis stage of explanation, however, there are no IPv6 multicast routerson the IPv6 network 121 or 122. Hence, the IP transmission/receptionmodule 2 does not receive this Hello message.

[0069] By performing these steps 201-204, the conversion device 1 nowknows the states of the multicast clients and routers on the networksconnected thereto. Then, the conversion device 1 sends the receivedmulticast packet to the networks requiring the multicast packet.

[0070] Next, in the communications network system 100, we will describea case where the IPv6 multicast client 104 is not a member of the IPv6multicast group (ffle::238.0.0.1).

[0071] First, let us explain about the processing performed by theconversion device 1 which has received an IPv4 multicast packet(destination: 238.0.0.1) sent from the IPv4 multicast server 101 out tothe IPv4 network 111.

[0072]FIG. 14 is a communication sequence diagram for steps 205-207.First, step 205 will be described. The IP transmission/reception module2 receives an IPv4 multicast packet (destination: 238.0.0.1) from theIPv4 network 111. Then, the IP transmission/reception module 2 inquiresof the IP multicast routing control information management module 6 therouting destination of the IPv4 multicast packet (IPv4 outputinformation and IPv6 output information) by using the IPv4 destinationaddress (=IP multicast address =238.0.0.1) and the IPv4 source address(=IP multicast server address =133.144.93.2) of the received IPv4multicast packet as a query key.

[0073] Next, step 206 of FIG. 14 will be explained. The IP multicastrouting control information management module 6 that received an inquirynow refers to the IP address conversion information holding module 4 forthe IPv6 addresses corresponding to the IPv4 destination address and theIPv4 source address.

[0074] Next, step 207 of FIG. 14 will be explained. The IP addressconversion information holding module 4 checks whether the inquired IPv4destination address is registered in the IP address conversion table 41and, if the corresponding IPv6 multicast address is already registered,reports that IPv6 multicast address to the source of inquiry (in thiscase, the IP multicast routing control information management module 6).When the IPv6 multicast address is found not registered, the IP addressconversion information holding module 4 matches the IPv4 destinationaddress to the IPv6 multicast address (ffle::238.0.0.1) which isproduced by adding fixed data, for example an IPv6 multicast prefix=ffle::/96, to the IPv4 destination address and then registers thecombination in the IP address conversion table 41. Then, the IP addressconversion information holding module 4 reports the IPv6 multicastaddress (ffle::238.0.0.1) to the IP multicast routing controlinformation management module 6.

[0075] The IP address conversion information holding module 4 alsochecks whether the IPv4 destination address is registered in the IPaddress conversion table 41 and, if the corresponding IPv6 unicastaddress is already registered, reports that IPv6 unicast address to thesource of inquiry (in this case, the IP multicast routing controlinformation management module 6). When the IPv6 unicast address is notregistered, the IP-address conversion information holding module 4retrieves an IPv6 unicast address from the conversion IP address holdingmodule 3, matches it with the IPv4 source address and then registers thecombination in the IP address conversion table 41. Then, the IP addressconversion information holding module 4 reports the IPv6 unicast addressto the IP multicast routing control information management module 6. Inthis stage of explanation, it is assumed that the IPv4 source address(133.144.93.2) is not registered in the IP address conversion table 41.Therefore, the IP address conversion information holding module 4retrieves an IPv6 unicast address (4::100) from the conversion IPaddress holding module 3, matches it with the IPv4 source address(133.144.93.2) and registers this combination in the IP addressconversion table 41. Then, the IP address conversion information holdingmodule 4 reports the IPv6 unicast address to the IP multicast routingcontrol information management module 6.

[0076]FIG. 15 is a communication sequence diagram for steps 208, 209.First, step 208 will be described. The IP multicast routing controlinformation management module 6 searches through the IP multicast pathinformation table 51 by using as a query key the IPv4 destinationaddress (IPv4 multicast address: 238.0.0.1) and the IPv4 source address(IPv4 multicast server address: 133.144.93.2) given by the IPtransmission/reception module 2. When the search finds the correspondingentry in the IP multicast path information table 51, the IP multicastrouting control information management module 6 notifies a packetoutputting interface and a protocol kind of the network connected tothat interface as output information to the IP transmission/receptionmodule 2. When on the other hand the corresponding entry is not found inthe IP multicast path information table 51, the IP multicast routingcontrol information management module 6 generates entries whose IPmulticast address is (238.0.0.1) and IP multicast server address is(133.144.93.2) described above.

[0077] Here, we will explain about the procedure for setting the outputinformation about the entries in the IP multicast path information table51 which is to be notified to the IP transmission/reception module 2,i.e., the information on the multicast packet outputting interface andon the protocol. The times when the IPv4 output information or IPv6output information about the IP multicast path information table 51 isset by using the table information as described below are when settingan initial value in the IP multicast path information table 51 at timesof starting the conversion device 1 or when adding a new IP multicastaddress in the IP multicast path information table 51 and setting aninitial value in the table.

[0078] For an interface for which the adjoining router information inthe IPv4 adjoining router information table 71 is set to “ON”, the IPmulticast routing control information management module 6 sets the IPv4output information in the IP multicast path information table 51 to“ON”. Similarly, for an interface for which the adjoining routerinformation in the IPv6 adjoining router information table 72 is set to“ON”, the IP multicast routing control information management module 6sets the IPv6 output information in the IP multicast path informationtable 51 to “ON”.

[0079] Next, the IP multicast routing control information managementmodule 6 refers to the IPv4 multicast member information table 61 todetermine an interface whose IPv4 address is (238.0.0.1) and whoseregistered member information is set to “ON”, and then sets the IPv4output information in the IP multicast path information table 51corresponding to that interface to “ON”. Similarly, the IP multicastrouting control information management module 6 refers to the IPv6multicast member information table 62 to determine an interface whoseIPv6 address is (ffle::238.0.0.1) and whose registered memberinformation is set to “ON”, and then sets the IPv6 output information inthe IP multicast path information table 51 corresponding to thatinterface to “ON”.

[0080] Further, the IP multicast routing control information managementmodule 6 sets to “OFF” the IPv4 output information in the IP multicastpath information table 51 corresponding to the interface that hasreceived the IPv4 multicast packet. The IP multicast routing controlinformation management module 6 also sets to “OFF” the IPv4 outputinformation and the IPv6 output information in the IP multicast pathinformation table 51 for the remaining interfaces. In this stage ofexplanation, the IP multicast routing control information managementmodule 6 notifies to the IP transmission/reception module 2 the outputinformation in the IP multicast path information table 51 in which theIPv4 output information for all interfaces is “OFF” and the IPv6 outputinformation for all interfaces is “OFF”.

[0081] Next, step 209 will be explained. The IP transmission/receptionmodule 2 sends an IPv4 multicast packet out to the IPv4 network that isconnected to the interface whose IPv4 output information given by the IPmulticast routing control information management module 6 is set to“ON”. In this stage of explanation, because the IPv4 output informationnotified to the IP transmission/reception module 2 is set to “OFF” forall interfaces, the IPv4 multicast packet is not sent out to any of theIPv4 networks.

[0082]FIG. 16 is a communication sequence diagram for steps 210-214. Instep 210, the IP transmission/reception module 2 transfers the IPv4multicast packet received to the IP header conversion module 5.

[0083] In step 211, the IP header conversion module 5 refers to the IPaddress conversion information holding module 4 for IPv6 addressescorresponding to the IPv4 destination address and IPv4 source address ofthe IPv4 multicast packet.

[0084] In step 212, the IP address conversion information holding module4 retrieves IPv6 addresses corresponding to the IPv4 destination addressand IPv4 source address from the IP address conversion table 41according to (step 207) and reports them to the source of inquiry (here,the IP header conversion module 5).

[0085] In step 213, the IP header conversion module 5 uses the IPv6multicast address corresponding to the IPv4 destination address that wasreported from the IP address conversion information holding module 4 toconvert the IPv4 destination address of the IPv4 multicast packet to theIPv6 multicast address. Similarly, the IP header conversion module 5uses the IPv6 address corresponding to the IPv4 source address toconvert the IPv4 source address to an IPv6 unicast address. This IPheader conversion processing generates an IPv6 multicast packet andreturns the generated IPv6 multicast packet to the IPtransmission/reception module 2.

[0086] In step 214, the IP transmission/reception module 2 sends thegenerated IPv6 multicast packet out to the IPv6 network connected to theinterface whose IPv6 output information given by the IP multicastrouting control information management module 6 in (step 208) is set to“ON”. In this stage of explanation, because the IPv6 output informationnotified is set to “OFF” for all interfaces, the IPv6 multicast packetis not sent to any of the IPv6 networks.

[0087] Next, a case will be described in which the IPv6 multicast client104 becomes a member of the IPv6 multicast group (ffle::238.0.0.1).

[0088] The IPv6 multicast client 104 generates an MLD Report message forparticipating in the IPv6 multicast group (ffle::238.0.0.1) according tothe MLD protocol and sends it to the IPv6 network 122. The processingperformed by the conversion device 1 that has received the MLD Reportmessage from the IPv6 network 122 will be described in the following.

[0089]FIG. 17 is a communication sequence diagram for step 215. In step215, first, the IP transmission/reception module 2 transfers thereceived MLD Report message to the IP multicast membership informationmanagement module 7. The IP multicast membership information managementmodule 7 analyzes the MLD Report message according to the MLD protocolto generate an IPv6 multicast member information table 62. Then, the IPmulticast membership information management module 7 notifies theinformation obtained through the analysis of the MLD Report message tothe IP multicast routing control information management module 6. The IPmulticast routing control information management module 6 generates theIP multicast path information table 51 based on the analyzed informationof the notified MLD message.

[0090] In this stage of explanation, it is found from the received MLDmessage that a member of the IPv6 multicast group (ffle::238.0.0.1)exists in the IPv6 network 122. Hence, according to the instruction fromthe IP multicast membership information management module 7, theinterface 11 in the IPv6 multicast member information table 62 with anIPv6 address of (ffle::238.0.0.1) is set to “ON ” and the interface 11in the IP multicast path information table 51 with an IPv6 address of(ffle::238.0.0.1) is set to “ON”. At this time, the IP multicast pathinformation table 51 may have a plurality of entries with the IPv6address of (ffle::238.0.0.1) depending on whether there are differing IPmulticast server addresses. In that case, the plurality of interfaces 11in these entries in the IPv6 multicast member information table 62 andthe IP multicast path information table 51 are set to “ON”.

[0091] Next, we will describe the processing performed after (step 215)by the conversion device 1 when it receives the IPv4 multicast packet(destination: 238.0.0.1) dispatched from the IPv4 multicast server 101.It is noted that the processing performed by the conversion device 1following (step 215) is done by repeating the above-described steps205-214. The details are given in the following.

[0092] The IP transmission/reception module 2 executes (step 205) torefer to the IP multicast routing control information management module6 for IPv4 output information and IPv6 output information representingthe routing destination of the received IPv4 multicast packet. The IPmulticast routing control information management module 6 performs (step206) to refer to the IP address conversion information holding module 4for IPv6 addresses corresponding to the IPv4 destination address andIPv4 source address.

[0093] The IP address conversion information holding module 4 performs(step 207) to retrieve the IPv6 addresses corresponding to the IPv4destination address and IPv4 source address of the IPv4 multicast packetand reports them to the source of inquiry (here, IP multicast routingcontrol information management module 6). In this stage of explanation,the IPv6 multicast address (ffle::238.0.0.1) corresponding to the IPv4destination address (238.0.0.1) and the IPv6 unicast address (4::100)corresponding to the IPv4 source address (133.144.93.2) are reported tothe IP multicast routing control information management module 6.

[0094] The IP multicast routing control information management module 6performs (step 208) to notify to the IP transmission/reception module 2the information on the interface for outputting the IPv4 multicastpacket and on the protocol of the network connected to that interface.In this stage of explanation, the IP multicast routing controlinformation management module 6 reports to the IP transmission/receptionmodule 2 the output information in which the IPv4 output information forall interfaces is “OFF”, the IPv6 output information for the interface11 is “ON ” and the IPv6 output information for the remaining interfacesis “OFF”.

[0095] The IP transmission/reception module 2 performs (step 209) toissue the IPv4 multicast packet to the IPv4 network connected to theinterface whose IPv4 output information is set to “ON”. In this stage ofexplanation, because the IPv4 output information is set to “OFF” for allinterfaces, the IPv4 multicast packet is not issued to any of the IPv4networks.

[0096] Next, the IP transmission/reception module 2, the IP addressconversion information holding module 4 and the IP header conversionmodule 5 perform (steps 210-213) to generate an IPv6 multicast packetfrom the IPv4 multicast packet.

[0097] The IP transmission/reception module 2 performs (step 214) toissue the generated IPv6 multicast packet to the IPv6 network connectedto the interface whose IPv6 output information notified by the IPmulticast routing control information management module 6 in (step 208)is set to “ON”. In the explanation of this embodiment, because the IPv6output information of the interface 11 is set to “ON”, the IPv6multicast packet is sent out to the IPv6 network 122 connected to theinterface 11. The IPv6 multicast client 104 receives the IPv6 multicastpacket dispatched from the conversion device 1 through the IPv6 network122.

[0098] This allows the multicast packet transmit by the IPv4 multicastserver 101 to the IPv4 network 111 to be received by the IPv6 multicastclient 104 on the IPv6 network 122.

[0099] Next, a case will be described in which the IPv6 multicast client104 leaves the IPv6 multicast group (ffle::238.0.0.1).

[0100] The IPv6 multicast client 104 generates an MLD Done message forleaving the IPv6 multicast group of (ffle::238.0.0.1) and sends it tothe IPv6 network 122. Then, the IPv6 multicast client 104 that hasdispatched the MLD Done message no longer receives a IPv6 multicastpacket with a destination address of (ffle::238.0.0.1) until itdispatches the MLD Report message again.

[0101] Here, the processing performed by the conversion device 1 thathas received the MLD Done message from the IPv6 network 122 will beexplained. FIG. 18 is a communication sequence diagram for step 217. Instep 217, the IP transmission/reception module 2 transfers the receivedMLD Done message to the IP multicast membership information managementmodule 7. Upon receiving the MLD Done message, the IP multicastmembership information management module 7 generates an MLD Querymessage for checking the existence of any member of the IPv6 multicastgroup with a multicast address of (ffle::238.0.0.1) and instructs the IPtransmission/reception module 2 to dispatch the MLD Query message to theIPv6 network 122. The IP transmission/reception module 2 then dispatchesthe MLD Query message to the IPv6 network 122.

[0102] If in the IPv6 network 122 there are other members of the IPv6multicast group, these members in response to the MLD Query message putout their MLD Report messages on the IPv6 network 122 within apredetermined period of time. In this case, the IPtransmission/reception module 2 transfers these MLD Report messages tothe IP multicast membership information management module 7. The IPmulticast membership information management module 7 thus recognizesthat other members of the IPv6 multicast group still exist on the IPv6network 122. Then, the IP multicast membership information managementmodule 7 discards the MLD Done message and continues transmitting theIPv6 multicast packet of (ffle::238.0.0.1) to the IPv6 network 122without performing the processing described later.

[0103] If there are no other members of the IPv6 multicast group, no MLDReport message indicating the participation in the IPv6 multicast groupis put on the IPv6 network 122 even with the elapse of a predeterminedtime. In this case, the IP multicast membership information managementmodule 7 generates an IPv6 multicast member information table 62according to the MLD Done message and notifies the information obtainedthrough the analysis of the MLD Done message to the IP multicast routingcontrol information management module 6. The IP multicast routingcontrol information management module 6 generates the IP multicast pathinformation table 51 according to the analysis information of thenotified MLD Done message.

[0104] That is, with the MLD Done message received and a series ofsubsequent steps performed, it is found that members of the IPv6multicast group (ffle::238.0.0.1) no longer exist on the IPv6 network122. So, the interface 11 in the IPv6 multicast member information table62 with an IPv6 address of (ffle::238.0.0.1) is set to “OFF” and theinterface 11 in the IP multicast path information table 51 with an IPv6address of (ffle::238.0.0.1) is set to “OFF”. The IP multicast pathinformation table 51 may have two or more entries with the IPv6 addressof (ffle::238.0.0.1) depending on whether there are differing IPmulticast server addresses. In that case, the plurality of interfaces 11in these entries are set to “OFF”.

[0105] Next, the processing performed after (step 217) by the conversiondevice 1 when it receives the IPv4 multicast packet (destination:238.0.0.1) dispatched by the IPv4 multicast server 101 onto the IPv4network 111 will be described. It is noted that the processing done bythe conversion device 1 following (step 217) is performed by repeatingthe above-described steps 205-214. This is detailed as follows.

[0106] The IP transmission/reception module 2 performs (step 205) torefer to the IP multicast routing control information management module6 for the IPv4 output information and IPv6 output informationrepresenting the routing destination of the IPv4 multicast packet. TheIP multicast routing control information management module 6 performs(step 206) to refer to the IP address conversion information holdingmodule 4 for IPv6 addresses corresponding to the IPv4 destinationaddress and IPv4 source address.

[0107] The IP address conversion information holding module 4 performs(step 207) to report the IPv6 addresses corresponding to the IPv4destination address and IPv4 source address of the IPv4 multicast packetto the source of inquiry (in this case, IP multicast routing controlinformation management module 6). In this stage of explanation, the IPv6multicast address (ffle::238.0.0.1) corresponding to the IPv4destination address (238.0.0.1) and the IPv6 unicast address (4::100)corresponding to the IPv4 source address (133.144.93.2) are reported.

[0108] The IP multicast routing control information management module 6performs (step 208) to notify to the IP transmission/reception module 2the information on the interface for outputting the IPv4 multicastpacket and on the protocol of the network connected to that interface.In this stage of explanation, the IP multicast routing controlinformation management module 6 notifies to the IPtransmission/reception module 2 the output information in which the IPv4output information for all interfaces is “OFF” and the IPv6 outputinformation for all interfaces is “OFF”.

[0109] The IP transmission/reception module 2 performs (step 209) todispatch the IPv4 multicast packet to the IPv4 network connected to theinterface whose IPv4 output information is set to “ON”. In this stage ofexplanation, because the IPv4 output information in the IP multicastpath information table 51 is set to “OFF” for all interfaces, the IPv4multicast packet is not dispatched to any of the IPv4 networks.

[0110] Next, the IP transmission/reception module 2, the IP addressconversion information holding module 4 and the IP header conversionmodule 5 perform (steps 210-213) to generate an IPv6 multicast packetfrom the received IPv4 multicast packet.

[0111] The IP transmission/reception module 2 performs (step 214) todispatch the generated IPv6 multicast packet to the IPv6 networkconnected to the interface whose IPv6 output information notified by theIP multicast routing control information management module 6 in (step208) is set to “ON”. In this stage of explanation, because the IPv6output information for all interfaces in the IP multicast pathinformation table 51 is set to “OFF”, the generated IPv6 multicastpacket is not sent out to any of the IPv6 networks.

[0112]FIG. 11 shows a configuration of a communications network system200 using the conversion device 1 according to this invention. Thecommunications network system 200 is connected to the IPv4 networks 111,112 and the IPv6 networks 121, 122 through the conversion device 1 (IPv4addresses: 133.144.97.1 and 133.144.98.1 and IPv6 addresses: 7::1 and8::1 are allocated, for example). Further, an IPv4 multicast router 105interconnects IPv4 networks 111 and 113, and an IPv4 multicast router106 interconnects IPv4 networks 112 and 114. An IPv6 multicast router107 interconnects IPv6 networks 121 and 123, and an IPv6 multicastrouter 108 interconnects IPv6 networks 122 and 124.

[0113] In the IPv4 network 113 there is an IPv4 multicast server 101(IPv4 address: 133.144.93.2) for transmitting IPv4-compatible multicastpackets. In the IPv4 network 114 there is an IPv4 multicast client 102(IPv4 address: 133.144.95-2) for receiving IPv4-compatible multicastpackets. In the IPv6 network 123 there is an IPv6 multicast server 103(IPv6 address: 1::2) for transmitting IPv6-compatible multicast packets.In the IPv6 network 124 there is an IPv6 multicast client 104 (IPv6address: 2::2) for receiving IPv6 -compatible multicast packets.

[0114] It is assumed that the IPv4 multicast server 101 is transmittingan IPv4 multicast packet (destination address: 238.0.0.1) to the IPv4network 113 and that the IPv6 multicast server 103 is transmitting anIPv6 multicast packet (destination address: ffle::238.0.0.2) to the IPv6network 123.

[0115] In this communications network system 200, we will describe acase where the IPv4 multicast server 101 transmits an IPv4 multicastpacket (IPv4 multicast address: 238.0.0.1) to the IPv4 network 113 andthe IPv6 multicast client 104 receives the IPv4 multicast packet. As tothe processing that overlaps those in the communications network system100 described above, some explanations will be omitted so as not to makethe discussion redundant.

[0116] First, let us explain about the processing (steps 201-204)periodically performed by the conversion device 1 according to the IGMPprotocol, the MLD protocol and the PIM-DM protocol.

[0117] The IP multicast membership information management module 7performs (step 201) to generate an IPv4 multicast member informationtable 61. In this stage of explanation, because there are no members ofthe IPv4 multicast group on the IPv4 networks 111, 112, the conversiondevice 1 does not receive an IGMP Report message. The IP multicastmembership information management module 7 also performs (step 202) togenerate an IPv6 multicast member information table 62. In this stage ofexplanation, because there are no members of the IPv6 multicast group onthe IPv6 networks 121, 122, the conversion device 1 does not receive anMLD Report message.

[0118] The IP multicast routing control information management module 6performs (step 203) to generate an IPv4 adjoining router informationtable 71. Here, the IPv4 adjoining router information table 71 isgenerated based on the information contained in a Hello message receivedfrom the IPv4 multicast routers 105, 106. That is, the IP multicastrouting control information management module 6 sets to “ON ” theadjoining router information in those entries in the IPv4 adjoiningrouter information table 71 that correspond to the interfaces 8, 9connected to the IPv4 networks 111, 112 where the IPv4 multicast routers105, 106 exist.

[0119] The IP multicast routing control information management module 6performs (step 204) to generate the IPv6 adjoining router informationtable 72. Here, the IPv6 adjoining router information table 72 isgenerated based on the information contained in a Hello message receivedfrom the IPv6 multicast routers 107, 108. That is, the IP multicastrouting control information management module 6 sets to “ON ” theadjoining router information in those entries in the IPv6 adjoiningrouter information table 72 that correspond to the interfaces 10, 11connected to the IPv6 networks 121, 122 where the IPv6 multicast routers107, 108 exist.

[0120] Next, a case where the IPv6 multicast client 104 is not a memberof the IPv6 multicast group (ffle::238.0.0.1) will be described.

[0121] First, the IPv4 multicast server 101 issues an IPv4 multicastpacket (destination: 238.0.0.1) to the IPv4 network 113. The IPv4multicast router 105 routes this IPv4 multicast packet to the IPv4network 111.

[0122] Here, we will explain the processing performed by the conversiondevice 1 that has received the IPv4 multicast packet from the IPv4network 111.

[0123] The IP transmission/reception module 2 performs (step 205) torefer to the IP multicast routing control information management module6 for IPv4 output information and IPv6 output information representingthe routing destination of the IPv4 multicast packet. The IP multicastrouting control information management module 6 performs (step 206) torefer to the IP address conversion information holding module 4 for IPv6addresses corresponding to the IPv4 destination address and IPv4 sourceaddress.

[0124] The IP address conversion information holding module 4 performs(step 207) to retrieve the IPv6 addresses corresponding to the IPv4destination address and IPv4 source address of the IPv4 multicast packetand reports them to the source of inquiry (here, IP multicast routingcontrol information management module 6). In this stage of explanation,the IPv6 multicast address (ffle::238.0.0.1) corresponding to the IPv4destination address (238.0.0.1) and the IPv6 unicast address (4::100)corresponding to the IPv4 source address (133.144.93.2) are reported tothe IP multicast routing control information management module 6.

[0125] The IP multicast routing control information management module 6performs (step 208) to notify to the IP transmission/reception module 2the information on the interface for outputting the IPv4 multicastpacket and on the protocol of the network connected to that interface.In this stage of explanation, because the IPv4 output information forthe interface 9 and the IPv6 output information for the interfaces 10and 11 in the IP multicast path information table 51 are “ON”, theseoutput information is notified from the IP multicast routing controlinformation management module 6 to the IP transmission/reception module2.

[0126] The IP transmission/reception module 2 performs (step 209) toissue the IPv4 multicast packet to the IPv4 network connected to theinterface whose IPv4 output information is reported to be set to “ON”.Here, because the IPv4 output information for the interface 9 in the IPmulticast path information table 51 is set to “ON”, the IPv4 multicastpacket is issued to the IPv4 network 112.

[0127] The IPv4 multicast router 106 receives the IPv4 multicast packet(destination: 238.0.0.1) issued from the conversion device 1 to the IPv4network 112. In the network system shown in FIG. 11, however, the IPv4network 114 has no member of the IPv4 multicast group specified by theIPv4 multicast address (238.0.0.1). Hence, the IPv4 multicast router 106discards the IPv4 multicast packet without forwarding it to the IPv4network 114.

[0128] Next, the IP transmission/reception module 2, the IP addressconversion information holding module 4 and the IP header conversionmodule 5 perform (steps 210-213) to generate an IPv6 multicast packetfrom the IPv4 multicast packet.

[0129] The IP transmission/reception module 2 performs (step 214) toissue the generated IPv6 multicast packet to the IPv6 network connectedto the interface whose IPv6 output information in the IP multicast pathinformation table 51 notified by the IP multicast routing controlinformation management module 6 in (step 208) is set to “ON”. In thisstage of explanation, because the IPv6 output information for theinterfaces 10, 11 in the IP multicast path information table 51 is setto “ON”, the IPv6 multicast packet is issued to the IPv6 networks 121,122.

[0130] The IPv6 multicast router 107 receives the IPv6 multicast packetissued from the conversion device 1 to the IPv6 network 121. In thenetwork system shown in FIG. 11, however, there is no member of the IPv6multicast group on the IPv6 network 123. So, the IPv6 multicast router107 discards the IPv6 multicast packet without forwarding it to the IPv6network 123.

[0131] Similarly, the IPv6 multicast router 108 receives the IPv6multicast packet issued from the conversion device 1 to the IPv6 network122. In the network system of FIG. 11, however, there is no member ofthe IPv6 multicast group on the IPv6 network 124. So, the IPv6 multicastrouter 108 discards the IPv6 multicast packet without forwarding it tothe IPv6 network 124.

[0132] Next, we will discuss the processing performed by the conversiondevice 1 that has received from the IPv6 multicast router 108 aPIM-Prune message requesting that the routing of the IPv6 multicastpacket (destination: ffle::238.0.0.1) to the IPv6 network 122 bestopped. The PIM-Prune message is a message transferred among routerswhich, by specifying an IP multicast address, or the destination addressof the IP multicast packet, requests the routers relaying the IPmulticast packet to stop routing the IP multicast packet using the IPmulticast address.

[0133]FIG. 19 is a communication sequence diagram for steps 231-233. Instep 231, the IP transmission/reception module 2 transfers the PIM-Prunemessage received from the IPv6 multicast router 108 to the IP multicastrouting control information management module 6. The IP multicastrouting control information management module 6 refers to the IP addressconversion information holding module 4 for the IPv4 addressescorresponding to the IPv6 multicast address and the IPv6 multicastserver address which are required by the PIM-Prune message not to berouted to the IPv6 network 122.

[0134] The IP address conversion information holding module 4 checks ifthe IPv6 multicast address (ffle::238.0.0.1) requested not to be routedto the IPv6 network 122 is registered in the IP address conversion table41. If the IPv6 multicast address is already registered, the IP addressconversion information holding module 4 reports the IPv4 addresscorresponding to the IPv6 multicast address to the source of inquiry(here, IP multicast routing control information management module 6). Ifthe IPv6 multicast address (ffle::238.0.0.1) is not registered in the IPaddress conversion table 41, the IP address conversion informationholding module 4 matches the IPv6 multicast address to the IPv4 address(238.0.0.1) which is obtained by eliminating the fixed data, for examplethe IPv6 multicast prefix (ffle::/96), from the IPv6 multicast address,registers them in the IP address conversion table 41, and reports themto the IP multicast routing control information management module 6. Thefixed data to be removed from the IPv6 multicast address is not limitedto the IPv6 multicast prefix (ffle::/96).

[0135] Next, the IP address conversion information holding module 4checks whether the IPv6 multicast server address (4::100) requested notto be routed to the IPv6 network 122 is registered in the IP addressconversion table 41. If the server address is already registered, the IPaddress conversion information holding module 4 reports the IPv4 addresssaved in the table in combination with the matching the IPv6 multicastserver address to the source of inquiry (here, the IP multicast routingcontrol information management module 6). When the IPv6 multicast serveraddress (4::100) is not registered, the IP address conversioninformation holding module 4 retrieves an IPv4 unicast address held inthe IPv4 unicast address table 31 of the conversion IP address holdingmodule 3. Then, the IP address conversion information holding module 4matches the retrieved IPv4 unicast address to the IPv6 multicast serveraddress (4::100), registers them in the IP address conversion table 41and then reports the IPv4 unicast address to the IP multicast routingcontrol information management module 6. In this stage of explanation,because the IPv4 address (133.144.93.2) and the IPv6 multicast serveraddress (4::100) are matched to each other and registered in the IPaddress conversion table 41, the IPv4 address of (133.144.93.2) isreported.

[0136] The IP multicast routing control information management module 6sets to “OFF” the IPv6 output for the interface, that has received thePIM-Prune message, in that entry in the IP multicast path informationtable 51 which has an IPv6 multicast address of (ffle::238.0.0.1) and anIPv6 multicast server address of (4::100). Further, the IP multicastrouting control information management module 6 sets to “OFF” the IPv6output for the interface, that has received the PIM-Prune message, inthat entry in the IP multicast path information table 51 whose IPmulticast address is the IPv4 address (238.0.0.1) reported from the IPaddress conversion information holding module 4 and whose IP multicastserver address is the reported IPv4 address (133.144.93.2). That is, inthis stage of explanation, the IPv6 output in the IP multicast pathinformation table 51 is set to “OFF” for the interface 11 that has(238.0.0.1) as the IP multicast address and (133.144.93.2) as themulticast server address.

[0137]FIG. 20 is a communication sequence diagram for step 234. In step234, when as a result of (step 233) there is an entry in the IPmulticast path information table 51 in which both the IPv4 output andthe IPv6 output are “OFF” for all interfaces, the IP multicast routingcontrol information management module 6 generates a PIM-Prune messagerequesting a multicast router not to forward the IP multicast packet ofthat entry. Then, the IP multicast routing control informationmanagement module 6 instructs the IP transmission/reception module 2 toissue the PIM-Prune message to the network that has a multicast routerwhich forwards the multicast packet from the multicast server to theconversion device 1. On receiving this instruction, the IPtransmission/reception module 2 issues the PIM-Prune message to thespecified network. In this stage of explanation, because as a result of(step 233) there is no path in the IP multicast path information table51 in which both the IPV4 output and IPV6 output are “OFF” for allinterfaces, the PIM-Prune message is not issued.

[0138] When it receives a PIM-Prune message from the IPv6 multicastrouter 107 requesting that the forwarding of the IPv6 multicast packet(destination: ffle::238.0.0.1) to the IPv6 network 121 be stopped or aPIM-Prune message from the IPv4 multicast router 106 requesting that theforwarding of the IPv4 multicast packet (destination: 238.0.0.1) to theIPv4 network 112 be stopped, the conversion device 1 performs theprocessing similar to (steps 231-234).

[0139] When it receives the PIM-Prune message from all the networksconnected, the conversion device 1 performs (step 233) to set to “OFF”the IPv4 output and IPv6 output for all interfaces in that entry in theIP multicast path information table 51 in which (238.0.0.1) isregistered as the IP multicast address and the address of the IPv4multicast server 101 (133.144.93.2) is registered as the IP multicastserver address. The IP multicast routing control information managementmodule 6 then generates an PIM-Prune message requesting that theforwarding of the IP multicast packet on that path be stopped andinstructs the IP transmission/reception module 2 to issue the PIM-Prunemessage to the IPv4 network 111 which has an upstream router on the pathfrom the conversion device 1 to the IPv4 multicast server 101, i.e., inthe case of the network of FIG. 11, the next pop router of the IPmulticast server address (133.144.93.2), or the IPv4 multicast router105. Then, the IP transmission/reception module 2 issues the PIM-Prunemessage to the specified network.

[0140] The PIM-Prune message is received by the IPv4 multicast router105. After this, the IPv4 multicast router 105 no longer forwards theIPv4 multicast packet with the destination address of (238.0.0.1) andthe source address of (133.144.93.2) to the IPv4 network 111.

[0141] Next, a case where the IPv6 multicast client 104 becomes a memberof the IPv6 multicast group (ffle::238.0.0.1) will be described.

[0142] The IPv6 multicast client 104 generates, according to the MLDprotocol, an MLD Report message to become a member of the IPv6 multicastgroup (ffle::238.0.0.1). When it receives the MLD Report message fromthe IPv6 network 124, the IPv6 multicast router 108 generates, accordingto the MLD protocol and PIM-DM protocol, a PIM Graft message requestinga router to forward a IPv6 multicast packet with a destination addressof (ffle::238.0.0.1) to the IPv6 network 124. The PIM Graft message is amessage which, by specifying the IP multicast address, or thedestination address of the IP multicast packet, requests a routerforwarding the IP multicast packet to forward an IP multicast packetusing that IP multicast address.

[0143] Here, we will described the processing performed by theconversion device 1 that has received the PIM Graft message from theIPv6 network 122. FIG. 21 is a communication sequence diagram for steps235-237. Let us first explain about step 235. The IPtransmission/reception module 2 receives the PIM Graft message issuedfrom the IPv6 multicast router 108 and transfers it to the IP multicastrouting control information management module 6. The IP multicastrouting control information management module 6 refers to the IP addressconversion information holding module 4 for the IPv4 addressescorresponding to the IPv6 multicast address and the IP multicast serveraddress, both of which are requested by the PIM Graft message to beforwarded to the IPv6 network 122.

[0144] Next, step 236 will be explained. The IP address conversioninformation holding module 4 checks if the IPv6 multicast address(ffle::238.0.0.1) requested to be forwarded to the IPv6 network 122 isregistered in the IP address conversion table 41. If the IPv6 multicastaddress is already registered, the IP address conversion informationholding module 4 reports the IPv4 multicast address saved in the tablein combination with the matching IPv6 multicast address to the source ofinquiry (here, IP multicast routing control information managementmodule 6). When the IPv6 multicast address (ffle::238.0.0.1) is notregistered, the IP address conversion information holding module 4matches the IPv6 multicast address (ffle:238.0.0.1) to the IPv4 address(238.0.0.1) which is obtained by eliminating the fixed data, for examplethe IPv6 multicast prefix (ffle::/96), from the IPv6 multicast address,registers them in the IP address conversion table 41, and reports themto the IP multicast routing control information management module 6. Thefixed data to be removed from the IPv6 multicast address is not limitedto the IPv6 multicast prefix of (ffle::/96).

[0145] Next, the IP address conversion information holding module 4checks whether the IPv6 multicast server address (4::100) requested tobe forwarded to the IPv6 network 122 is registered in the IP addressconversion table 41. If the server address is already registered, the IPaddress conversion information holding module 4 reports the IPv4 addresssaved in the table in combination with the matching the IPv6 multicastserver address to the source of inquiry (here, the IP multicast routingcontrol information management module 6). When the IPv6 multicast serveraddress is not registered, the IP address conversion information holdingmodule 4 retrieves an IPv4 unicast address from the conversion IPaddress holding module 3. Then, the IP address conversion informationholding module 4 matches the retrieved IPv4 unicast address to the IPv6multicast server address, registers them in the IP address conversiontable 41 and then reports the IPv4 unicast address to the source ofinquiry (here, the IP multicast routing control information managementmodule 6). In this stage of explanation, because the IPv6 multicastserver address (4::100) is matched to the IPv4 address (133.144.93.2)and registered in the IP address conversion table 41, the IPv4 addressof (133.144.93.2) is reported to the IP multicast routing controlinformation management module 6.

[0146] Next, step 237 will be described. The IP multicast routingcontrol information management module 6 sets to “ON” the IPv6 output forthe interface, that has received the PIM Graft message, in that entry inthe IP multicast path information table 51 which has an IPv6 multicastaddress of (ffle::238.0.0.1) and an IPv6 multicast server address of(4::100). Further, the IP multicast routing control informationmanagement module 6 sets to “ON” the IPv6 output for the interface, thathas received the PIM Graft message, in that entry in the IP multicastpath information table 51 which is registered with the IPv4 address(238.0.0.1) reported from the IP address conversion information holdingmodule 4 and with the reported IPv4 address (133.144.93.2). In thisstage of explanation, the IPv6 output for the interface 11 in an entrywhich has an IPv4 address of (238.0.0.1) and an IPv4 address of(133.144.93.2) is set to “ON”.

[0147]FIG. 22 is a communication sequence diagram for step 238. In step238, if as a result of (step 237) there is any path for which the IPv4output or IPv6 output in the IP multicast path information table 51 is“ON”, the IP multicast routing control information management module 6generates a PIM Graft message requesting a router to forward an IPmulticast packet on that path.

[0148] In this explanation, as a result of (step 237), the IPv6 outputfor the interface 11 in that entry in the IP multicast path informationtable 51 whose IP multicast address is (238.0.0.1) and IP multicastserver address is (133.144.93.2) is set to “ON”. Hence, the IP multicastrouting control information management module 6 generates a PIM Graftmessage requesting a router to forward an IPv4 multicast packet with andestination address of (238.0.0.1) and a source address of(133.144.93.2) to the IPv4 network 111. Then, the IP multicast routingcontrol information management module 6 instructs the IPtransmission/reception module 2 to issue the PIM Graft message to theIPv4 network 111 which has an upstream router on the path from theconversion device 1 to the IPv4 multicast server 101, i.e., in the caseof the network of FIG. 11, the next pop router of the IPv4 multicastserver address (133.144.93.2), or the IPv4 multicast router 105. The IPtransmission/reception module 2 then issues the PIM Graft message to thespecified network.

[0149] The PIM Graft message is received by the IPv4 multicast router105. After this, the IPv4 multicast router 105 forwards to the IPv4network 111 an IPv4 multicast packet that has the IPv4 multicast address(238.0.0.1) as the destination address and the IPv4 multicast serveraddress (133.144.93.2) as the source address.

[0150] Next, a case where the IPv6 multicast client 104 leaves the IPv6multicast group (ffle::238.0.0.1) will be explained.

[0151] The IPv6 multicast client 104 generates, according to the MLDprotocol, an MLD Done message for leaving the IPv6 multicast group(ffle::238.0.0.1) and issues it to the IPv6 network 124. Upon receivingthe MLD Done message from the IPv6 network 124, the IPv6 multicastrouter 108 generates, according to the MLD protocol and PIM-DM protocol,a PIM-Prune message requesting a router not to forward an IPv6 multicastpacket with the destination address of (ffle::238.0.0.1) to the IPv6network 124 and issues the generated PIM-Prune message to the IPv6network 122.

[0152] The conversion device 1, when it receives the PIM-Prune messagefrom the IPv6 network 122, performs (steps 231-234) to stop the routing.If there are no other networks that require the IPv6 multicast packetwith the destination address of (ffle::238.0.0.1) to be forwarded, theconversion device 1 generates a PIM-Prune message calling for thesuspension of routing and issues the generated PIM-Prune message to theupstream router on the path, or the IPv4 multicast router 105. Afterthis, the IPv4 multicast router 105 no longer forwards the IPv4multicast packet transmit by the IPv4 multicast server 101 to the IPv4network 111.

[0153] In the explanation above, we have described a case where an IPv4multicast packet with an IPv4 multicast address (238.0.0.1) transmit bythe IPv4 multicast server 101 is received by the IPv6 multicast client104. Performing the similar processing also allows an IPv6 multicastpacket with an IPv6 multicast address (ffle::238.0.0.2) transmit by theIPv6 multicast server 103 to be received by the IPv4 multicast client102.

[0154] Further, in the explanation above, we have described a case wherethe conversion from the IPv4 multicast packet transmit by the IPv4multicast server 101 into the IPv6 packet is done by adding a fixedpattern to the higher order place of the IPv4 destination address(238.0.0.1) to obtain a converted 128-bit IPv6 address, for example(ffle::ffff.238.0.0.1). Other methods may be used. For example, it ispossible to hold in advance in the conversion IP address holding module3 the IPv4 multicast address and IPv6 multicast address used for IPheader conversion in addition to the IPv4 unicast address and IPv6unicast address and to retrieve the converted IPv6 multicast address,for example (ffle::100), from the conversion IP address holding module3. Further, the conversion device may communicate with the DHCP serverto automatically retrieve unused addresses and hold them in theconversion IP address holding module 3.

[0155] In the embodiment above, we have described a case where theconversion device 1 reflects on the IPv6 multicast routing controlinformation the IPv4 multicast routing control information obtained fromthe adjoining IPv4 multicast router and then exchanges this IPv6multicast routing control information with the adjoining IPv6 multicastrouter to forward the IP multicast packet transmit by the IPv6 multicastserver 103 to the IPv4 multicast client 102. We have also described acase where the conversion device 1 reflects on the IPv4 multicastrouting control information the IPv6 multicast routing controlinformation obtained from the adjoining IPv6 multicast router and thenexchanges this IPv4 multicast routing control information with theadjoining IPv4 multicast router to forward the IP multicast packettransmit by the IPv4 multicast server 101 to the IPv6 multicast client104. The routing described above can also be achieved in other ways. Forexample, the IPv6 multicast routing control information necessary forforwarding the IP multicast packet transmit by the IPv6 multicast server103 to the IPv4 multicast client 102 may be set in the conversion device1 by an administrator. Alternatively, the IPv4 multicast routing controlinformation necessary for forwarding the IP multicast packet transmit bythe IPv4 multicast server 101 to the IPv6 multicast client 104 may beset in the conversion device 1 by an administrator.

[0156] Further, the IP address conversion information holding module 4may delete those of the matching combinations of the IPv4 address andthe IPv6 address which are not referenced for a predetermined period oftime, and then return the deleted IPv4 unicast addresses and IPv6unicast addresses to the conversion IP address holding module 3.

[0157] As described above, according to the present invention the IPv6terminals can receive IP multicast packets transmit by the IPv4terminals, and the IPv4 terminals can receive IP multicast packetstransmit by the IPv6 terminals.

What is claimed is:
 1. A method of routing at least one IPv4 multicastpacket transmitted through an IPv4 network to at least one IPv6 network,the method comprising the steps of: storing in memory the at least oneIPv6 network, or a routing destination of the at least one IPv4multicast packet; receiving the at least one IPv4 multicast packet;converting an IPv4 header of the received IPv4 multicast packet into anIPv6 header and generating an IPv6 multicast packet; and transmittingthe generated IPv6 multicast packet to the IPv6 network stored inmemory.
 2. The method according to claim 1, wherein the step of storingthe IPv6 network in memory matches at least a destination address of theIPv4 multicast packet to information for identifying the at least oneIPv6 network and stores them in memory.
 3. The method according to claim1, further comprising the steps of: storing in memory another IPv4network, or a routing destination of the at least one IPv4 multicastpacket; and transmitting the at least one IPv4 multicast packet to theother IPv4 network stored in memory.
 4. The method according to claim 1,further comprising the steps of: receiving from the at least one IPv6network a message requesting a reception of the generated IPv6 multicastpacket.
 5. A method of routing an IPv4 multicast packet transmittedthrough an IPv4 network to one or more IPv6 networks, the methodcomprising the steps of: receiving from an arbitrary one of the one ormore IPv6 networks a message requesting a reception of an IPv6 multicastpacket; storing in memory the arbitrary IPv6 network as a networktransmitting the IPv6 multicast packet; receiving the IPv4 multicastpacket; converting the received IPv4 multicast packet into the IPv6multicast packet; and transmitting the IPv6 multicast packet to the IPv6network stored in memory.
 6. The method according to claim 5, whereinthe step of storing the arbitrary IPv6 network in memory matches atleast a destination address of the IPv4 multicast packet to informationfor identifying the arbitrary IPv6 network and stores them in memory. 7.The method according to claim 5, further comprising the steps of:receiving a message requesting a reception of the IPv4 multicast packetfrom another IPv4 network; storing in memory the IPv4 network that hastransmitted the message; and transmitting the received IPv4 multicastpacket to the IPv4 network stored in memory.
 8. The method according toclaim 5, further comprising the steps of: receiving from the arbitraryIPv6 network a message indicating a suspension of the reception of theIPv6 multicast packet; and storing in memory the arbitrary IPv6 networkas a network to which the IPv6 multicast packet is not transmitted.
 9. Amethod of routing each of a plurality of IPv4 multicast packetstransmitted through an IPv4 network to a plurality of IPv6 networks, themethod comprising the steps of: receiving from an arbitrary one of theplurality of IPv6 networks a message requesting a reception of an IPv6multicast packet; when the IPv6 multicast packet the reception of whichhas been requested is generated by conversion of one of the plurality ofIPv4 multicast packets, matching the arbitrary IPv6 network that hastransmitted the message with a part of header information of the oneIPv4 multicast packet and storing them in memory, the arbitrary IPv6network being taken as a network requesting the reception of the IPv6multicast packet; receiving one of the plurality of IPv4 multicastpackets; converting the received IPv4 multicast packet into the IPv6multicast packet; and transmitting the IPv6 multicast packet that wasgenerated by the conversion to the IPv6 network that was matched with apart of the header information of the received IPv4 multicast packet andwhich was stored in memory.
 10. The method according to claim 9, furthercomprising the step of: transmitting to the plurality of IPv6 networks amessage for checking the existence of a terminal requesting thereception of the IPv6 multicast packet.
 11. The method according toclaim 9, further comprising the steps of: receiving from a terminalconnected to an arbitrary one of the plurality of IPv6 networks amessage indicating that the reception of the IPv6 multicast packet isnot required; and when a terminal requesting the reception of the IPv6multicast packet no longer exists on the arbitrary one of the IPv6networks, matching the arbitrary one of the IPv6 networks with a part ofthe header information and storing them in memory, the arbitrary one ofthe IPv6 networks being taken as a network not requiring the receptionof the IPv6 multicast packet.
 12. The method according to claim 9,further comprising the steps of: receiving from at least one IPv4network a message requesting the reception of the one IPv4 multicastpacket; and matching the at least one IPv4 network with a part of theheader information and storing them in memory, the at least one IPv4network being taken as a network transmitting the one IPv4 multicastpacket.
 13. The method according to claim 9, wherein the part of theheader information includes a destination address of at least the oneIPv4 multicast packet.
 14. A method of routing an IPv4 multicast packettransmitted from a router on an IPv4 network to an IPv6 network, themethod comprising the steps of: storing in memory at least one IPv6network routing the IPv4 multicast packet; receiving the IPv4 multicastpacket transmitted from the router; converting the received IPv4multicast packet into an IPv6 multicast packet; and transmitting theIPv6 multicast packet to the at least one IPv6 network stored in memory.15. The method according to claim 14, further comprising the steps of:receiving from the at least one IPv6 network a message requesting asuspension of the reception of the IPv6 multicast packet; and when anIPv6 network requiring a routing of the IPv4 multicast packet no longerexists, transmitting to the router a message requesting a suspension ofthe routing of the IPv4 multicast packet.
 16. The method according toclaim 14, further comprising the steps of: storing in memory at leastone IPv4 network routing the received IPv4 multicast packet; andtransmitting the received IPv4 multicast packet to the IPv4 network theIPv4 network stored in memory.
 17. The method according to claim 15,further comprising the steps of: receiving from the at least one IPv6network a message requesting a transmission of the IPv4 multicast packettransmitted from the router; and transmitting to the router a messagerequesting a routing of the IPv4 multicast packet.
 18. A method ofrouting each of a plurality of IPv4 multicast packets routed by a routeron an IPv4 network to one or more IPv6 networks, the method comprisingthe steps of: matching each address information of the plurality of IPv4multicast packets with the one or more IPv6 networks, or routingdestinations of the plurality of IPv4 multicast packets, and storingthem in memory; receiving one of the plurality of IPv4 multicast packetstransmitted from the router; converting the received IPv4 multicastpacket into an IPv6 multicast packet; and transmitting the IPv6multicast packet to the IPv6 network matched with the received IPv4multicast packet and stored in memory.
 19. The method according to claim18, further comprising the steps of: receiving from one of one or moreIPv6 networks a message requesting a suspension of a routing of the IPv6multicast packet; and when an IPv6 network requiring the routing of theIPv4 multicast packet no longer exists, transmitting to the router amessage requesting the suspension of the routing of the IPv4 multicastpacket.
 20. The method according to claim 19, further comprising thesteps of: receiving from an arbitrary one of the IPv6 networks a messagerequesting a routing of the IPv6 multicast packet; and transmitting tothe router a message requesting a suspension of the routing of the IPv4multicast packet.
 21. The method according to claim 18, furthercomprising the steps of: matching each address information of theplurality of IPv4 multicast packets with the IPv4 networks, or routingdestinations of the plurality of IPv4 multicast packets, and storingthem in memory; and transmitting the received IPv4 multicast packet tothe IPv4 network stored in memory.